The NKG2D receptor also contributes to immune surveillance, as illustrated by increased tumor incidence in NKG2D-deficient mice.53 Most solid tumors as well as leukemias express at least one of the eight NKG2D ligands (MHC class I-related chain A/B [MICA/B], UL16-binding proteins [ULBP1–6]),54 and the cytotoxic effector function of γδ T cells can be triggered through NKG2D/NKG2D ligand interactions independent of TCR signaling.16,55 Notably, however, NKG2D ligands are not uniformly expressed on malignant cells. This evidence concerns the gene KLRK1 and leukemia.